Saltwater Fish Compatibility Guide: Quick Reference Table by Aggression & Size

Keeping saltwater fish in mixed-species tanks is said to be more challenging than freshwater aquaria. This is because territorial instincts, aggression levels, and feeding habits vary significantly by species. Improper combinations can result in weaker individuals being bullied and, in worst cases, dying. However, with proper knowledge, creating a beautiful mixed-species saltwater tank is entirely achievable. This article breaks down compatibility into three key axes—aggression, size, and diet—and provides specific examples of popular species combinations.

Three Factors That Determine Compatibility

When evaluating saltwater fish compatibility, assess each species along the following three axes:

① Aggression & Territorial Behavior Many saltwater fish display strong aggression toward their own or closely related species. Butterfly fish and damselfish, in particular, defend territories fiercely. It's helpful to categorize aggression levels as "high," "medium," or "low."

② Body Size Differences When there's a significant size gap, larger fish may predate on smaller ones. As a general rule, a body length difference of 3x or greater introduces predation risk.

③ Feeding Habits (Carnivorous, Herbivorous, Omnivorous) Carnivorous fish target small fish and crustaceans. Herbivorous fish consume algae on live rock and benefit tank conditions, though they may compete for the same feeding grounds. Different feeding habits can reduce competition, but carnivorous species require extra caution when mixing.

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Compatibility Quick Reference Table by Aggression & Size

Use the table below where "〇 = Easy to mix," "△ = Conditional compatibility," and "× = Difficult to mix."